MODS For Soundcraft 400b Input Modules
Old 3rd November 2010
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MODS For Soundcraft 400b Input Modules

Hey guys Im a about to start on my 400B 10 channel frontend project and wanted to know if anyone knows any good mods they can post here?
Im Going to change all electrolytic caps to Panasonic FM and FC
The other capacitors Im going to replace with Polypropolyne caps.
Jim Williams posted a Ground compensated Direct out Mod- His Post

It's very easy to add direct outs to these. Get some shielded cable, tac at the fader amp's output. Drill and mount isolated 1/4 " stereo jacks. Run the shielded cable to the jack and wire the "tip" to the cable hot. Run a 75 ohm resistor from the "ring" to ground. Tie the jack's ground lug to the input ground, not the buss ground. You now have ground compensated, asymetrical balanced direct outputs!

Jim Williams
Audio Upgrades

Anything else I can do to Hot Rod these Guys?
Schematics are attached.....
Attached Files
File Type: pdf 400B_Schems.PDF (1.14 MB, 640 views)
Old 3rd November 2010
  #2
Try swapping C7 to 1000uf. IC1 to LM6172 and C8/C9 to 22pf.
I did those mods on a D&R (similar schematic) and i made a big difference. I A/B'd it. Less low mid mud and clearer highs wich made the sound more upfront and clear. Don't forget the two psu bypass caps (0,1nf) to stabilize the opamp.

You can also try to work the circuit and rewire it to a transamp. Didn't try that myself because phase reversal switch is located between the input transistor pair and the opamp, on my D&R.

Good luck.
Old 3rd November 2010
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Quote:
Originally Posted by Aerophone View Post
Try swapping C7 to 1000uf. IC1 to LM6172 and C8/C9 to 22pf.
I did those mods on a D&R (similar schematic) and i made a big difference. I A/B'd it. Less low mid mud and clearer highs wich made the sound more upfront and clear. Don't forget the two psu bypass caps (0,1nf) to stabilize the opamp.

You can also try to work the circuit and rewire it to a transamp. Didn't try that myself because phase reversal switch is located between the input transistor pair and the opamp, on my D&R.

Good luck.
Hey Thanx for the Info on the mods. The LM6172 , I looked it up, says that it is optimized for +/-15v, is this ok for +/-17v?
Old 4th November 2010
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I found these on another site...............
Re: Any Soundcraft 200B users?

by outoftune on Mon Aug 10, 2009 7:20 pm
hey, i was going to pm you about this, but figured i would post it here in case others are interested.

here are the mods that i have done to my 400b (24 X 4 X 2).

1) star grounding mod ala eddie ciletti: http://www.tangible-technology.com/articles/200b.html

2) fully recapped, upgraded the 47uf signal path caps to 220uf Nichicon PW with a 0.1uf wima bypass on the backside of the pcb. upgraded the 100uf in the mic pre to 1000uf nichicon HE for better LF response at high gains.

3) upgraded the mic pre transistors to 2sa970's. (not sure what's in the 200b, mine had pn4355's. NOTE: the 2sa970's had a different pinout so i had to reorient the transistor and bend/heatshrink the legs)

4) build a new high current psu (+/- 17v @ 3A) out of a Power One module i got on ebay ($5 surplus!!) breadboarded the 48v circuit.

5) upgraded the tl072 opamps to burr brown opa2134's and the tl071's to opa604's. added 0.1uf ceramic caps to the power rails of each opamp and install a mill max machined socket for each opamp.

i have a couple other things i plan to do once i finish the last few channels of opamps. i have a pair of john hardy 990's that i am going to install as the summing amps. this isn't too hard, just need to find time. i emailed with john hardy himself and he gave me a few suggestions and tips. great guy.

overall, i'm pretty happy with this board right now. it's the first real board i've had, so i don't have much to compare it against. it has been extremely easy to work on and that is a huge plus for me. let me know if anyone has any questions.
Old 4th November 2010
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I would advice against replacing TL072 FET opamps with LM6172 bipolars. Didn't work out well in my 200B, even with additional local bypassing. High end sounds strange (though I couldn't detect oscillation). To replace FET opamps I think the AD8512 sounds best, OPA827 is great, too, but pricy and only availible for singles.
Old 4th November 2010
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Originally Posted by living sounds View Post
I would advice against replacing TL072 FET opamps with LM6172 bipolars. Didn't work out well in my 200B, even with additional local bypassing. High end sounds strange (though I couldn't detect oscillation). To replace FET opamps I think the AD8512 sounds best, OPA827 is great, too, but pricy and only availible for singles.
Thanx for the info, I am a bit ignorant in my electronics knowledge, but want to learn, so some of the terminology, like local bypassing just flys right over my head.
Is the AD8512 a drop in replacement, or are there other mods I must do to make this opamp work. Also Im using these strips just for the Mic preamp, line in, and eq section. No bussing will be used, or connected. So with that said do I have to replace all the IC's or just the one for the mic preamp?
Thanx for all the great posts, I appreciate any info or help I can get
Old 4th November 2010
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Also, with Change on the electrolytics, from 47uf to 220uf, does the voltage choice remain the same? EX- 47uf/63v do I change this to 220uf/63v?
Old 6th November 2010
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Pics Of the Chassis

Started building the case, about a hour and ahalf into it now. Aluminum Chassis, fabricated from scratch, no drawings to go off just measurements.
Attached Thumbnails
MODS For Soundcraft 400b Input Modules-dscn0239.jpg   MODS For Soundcraft 400b Input Modules-dscn0240.jpg   MODS For Soundcraft 400b Input Modules-dscn0241.jpg   MODS For Soundcraft 400b Input Modules-dscn0242.jpg   MODS For Soundcraft 400b Input Modules-dscn0243.jpg  

Old 6th November 2010
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Quote:
Originally Posted by The Convicted View Post
Thanx for the info, I am a bit ignorant in my electronics knowledge, but want to learn, so some of the terminology, like local bypassing just flys right over my head.
Is the AD8512 a drop in replacement, or are there other mods I must do to make this opamp work. Also Im using these strips just for the Mic preamp, line in, and eq section. No bussing will be used, or connected. So with that said do I have to replace all the IC's or just the one for the mic preamp?
Thanx for all the great posts, I appreciate any info or help I can get
Take a look at the schematics, it all depends on the signal flow. As for local bypassing, you can find a lot of info about that here and at prodigy-pro.
Old 6th November 2010
  #10
local bypass is a must if you want to play with new opamps. it's easy to do.
I'm pretty sure lm6172 will work on the preamp section. Your circuit is almost the same as my D&R, only diferrence is in the opamp feedback resitors but is a little difference. my d&r is running 12 Lm6172s at 17v. they run cool and smooth and made big difference, YMMV.
Old 7th November 2010
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living

sounds


Member

Posts: 514





Found This LIVING SOUNDS..........




Re: Which Soundcraft Mixer Sounds Cool?
« Reply #8 on: December 30, 2009, 11:49:31 am »

In the past 2 months I've gradually recapped and modded a 200B. It sounds OK stock, EQs are useable, far better than the cheap new chinese mixers, but lacking clarity, loosing bass and eating up transients. Now, with the grounding mod, (mostly) bigger Panasonic FM caps + Wima bypass caps (in the signal path), all power resistors reduced to 10 ohm, the EQ modded and with better caps and the op amps biased into class A via 3.3k resistors it sounds better than I would have believed possible. I don't even see a need to replace the TL072/071 op amps on the channels or 5532 on the master bus/busses.
The 200B or Delta 200 are great to work on because of the modular structure and high quality mechanical parts.
Old 7th November 2010
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So bypassing a electrolytic capacitor, you just solder the .01 Wima cap to the back side of the PCB of the Electro Cap?

I probably will not change the IC's because I have no experience with circuit rework. But I will change the electros with bigger values and bypass them with wima caps. Ill change the transistors, and Use Wima caps for the eq section. And that is as far as I will most likely take it on my own.
Old 7th November 2010
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Originally Posted by The Convicted View Post
So bypassing a electrolytic capacitor, you just solder the .01 Wima cap to the back side of the PCB of the Electro Cap?

I probably will not change the IC's because I have no experience with circuit rework. But I will change the electros with bigger values and bypass them with wima caps. Ill change the transistors, and Use Wima caps for the eq section. And that is as far as I will most likely take it on my own.

Yes, but use 100nf if you can. Polypropylene (metallized, since pure PP would be too big). CMK caps are great too, if you can find them (at a surplus most likely, since they're no longer made).

In the EQ section the better caps sound better as well, use (pure, not metallized) polyproylene for the high end nad metallized pp for the rest. I've also changed all the EQ values to more usefull ones with different caps and resistors.

Biasing into Class A made quite a difference, too, but you need to upgrade the power supply for that. Better op amps make a big difference, I wouldn't want a TL072 in the signal path anywhere. The local bypassing is a must for some of the faster op amps, but a 5532 will profit from that as well. Just solder 100nf NPO ceramics from ground to +, - , and between the two right at the op amps.


It was a lot of work and trial and error, but now my console sounds great. I wasn't even close to getting finished with it when I wrote that post at prodigy. ;-)
Old 7th November 2010
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Ill be using a JLM audio Powerstation (3A per rail) with a 63a or 80va transformer. I emailed Joe from JLM inquiring about his power supplies, and he assured me that even with IC upgrades and mods these strips wouldnt draw much current.
Old 7th November 2010
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Ill be using a JLM audio Powerstation (3A per rail) with a 63a or 80va transformer. I emailed Joe from JLM inquiring about his power supplies, and he assured me that even with IC upgrades and mods these strips wouldnt draw much current.
According to their website you get 1.5A per rail. That's only a little more than the CPS-150's 1.25A.
Old 7th November 2010
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Hmmmmmmm...........
Well, when I spoke to him, he said it would work. I thought that it was a 3a per rail, until I saw the (1.5a per regulated output). Well I ll give it a shot, already ordered it so, thats that. If I need to build another supply, I could use this for my other projects!
Old 7th November 2010
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Originally Posted by living sounds View Post
Yes, but use 100nf if you can. Polypropylene (metallized, since pure PP would be too big). CMK caps are great too, if you can find them (at a surplus most likely, since they're no longer made).

In the EQ section the better caps sound better as well, use (pure, not metallized) polyproylene for the high end nad metallized pp for the rest. I've also changed all the EQ values to more usefull ones with different caps and resistors.

Biasing into Class A made quite a difference, too, but you need to upgrade the power supply for that. Better op amps make a big difference, I wouldn't want a TL072 in the signal path anywhere. The local bypassing is a must for some of the faster op amps, but a 5532 will profit from that as well. Just solder 100nf NPO ceramics from ground to +, - , and between the two right at the op amps.


It was a lot of work and trial and error, but now my console sounds great. I wasn't even close to getting finished with it when I wrote that post at prodigy. ;-)
My first project I did was an Allen and heath System 8, it is loaded with TL072 ICs, The sound is dark, loads of character but not very clean. I upgraded all the caps with Panasonic FM and FCs and channel 1-6 all the other caps are replaced with wima polyester and polypropolyne caps. The Eq really benefited from it.

I would like to really get the most out of this 400b, Id like to get my hands on a mastersection so this will be like a 8x2 mixer so I can sum on it as well.
Im thinking about sending a channel to Audio Upgrades, and copying them to my other channels. Or try to figure this out.....we'll see
Old 8th November 2010
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Heres some more pics, know with the XLR and TRS jacks drilled out, I will most likely add another row of TRS jacks for insert points. also the strips (8 of them) are mounted with M4 nutserts.
Attached Thumbnails
MODS For Soundcraft 400b Input Modules-dscn0244.jpg   MODS For Soundcraft 400b Input Modules-dscn0247.jpg  
Old 10th November 2010
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Quote:
Originally Posted by living sounds View Post
I would advice against replacing TL072 FET opamps with LM6172 bipolars. Didn't work out well in my 200B, even with additional local bypassing. High end sounds strange (though I couldn't detect oscillation). To replace FET opamps I think the AD8512 sounds best, OPA827 is great, too, but pricy and only availible for singles.

Ok I found some SOIC to 8 DIP adapters from Brown Dog.
Should I replace the eq section TL072 as well?
Old 11th November 2010
  #20
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I've got a soundcraft 24 channel soundcraft 400b that I can't decide if I should keep and "fix up" (which I have 0 experience doing) or if I should try to sell it...

Are the preamps / eq in this board really "that good" would I see a benefit using these and perhaps summing through the board when my interface is a lowly presonus firestudio? Are the preamps in the 400b much "better"?

what to do, what to do...

(sorry to clog you thread, but just wanted to get some input from 400b users)
Old 14th November 2010
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I get it now...Local Bypass, found in another Post

Add a pair of .1 uf mono ceramic caps from pins 4 and 8 to a close by ground. Now you can play with opamps.

Jim Williams
Audio Upgrades
Old 14th November 2010
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Question

Quote:
Originally Posted by The Convicted View Post
Im Going to change all electrolytic caps to Panasonic FM and FC

Anything else I can do to Hot Rod these Guys?
Schematics are attached.....
why Panasonic?
why not mod each module with different brand of electrolitic?

one module with nichicon k
other with elna silmic2
other with Panasonic
other with BlackGate
other with Rubycon...
other with fine gold...
etc...

using Cardas Tri Eutectic silver.
Old 14th November 2010
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Dont Know why,
I like consistency I guess, I liked FMs and FCs after my System 8 rebuild.
Old 14th November 2010
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Originally Posted by JuanPabloCuervo View Post
why Panasonic?
why not mod each module with different brand of electrolitic?

one module with nichicon k
other with elna silmic2
other with Panasonic
other with BlackGate
other with Rubycon...
other with fine gold...
etc...

using Cardas Tri Eutectic silver.
Easy, they're great and cheap and take a long time to go bad. Add a bypass cap in the signal path and you're fine. Everything else is a waste of money given the cost of the console IMO.
Old 14th November 2010
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Question

Quote:
Originally Posted by living sounds View Post
Easy, they're great and cheap and take a long time to go bad. Add a bypass cap in the signal path and you're fine. Everything else is a waste of money given the cost of the console IMO.
sanyo os con last more..
its not about time its about sound.
Old 14th November 2010
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Originally Posted by JuanPabloCuervo View Post
sanyo os con last more..
its not about time its about sound.
Yes, Black Gates sound better, but with the bypass caps the difference isn't that big and you'd spend a fortune and will have to recap it a lot sooner. And again, the caps are far from the only limiting factor in the console. It would make a lot more sense to use op amps with negligeable DC offset and remove the caps.
Old 14th November 2010
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Quote:
Originally Posted by The Convicted View Post
Add a pair of .1 uf mono ceramic caps from pins 4 and 8 to a close by ground. Now you can play with opamps.

Jim Williams
Audio Upgrades
Now one last thing about this, Do I tie pins 4 and 8 together with a .01 ceramic cap and then to a near by ground with another .01 cap, or do I individually tie them into a near by ground?
Old 14th November 2010
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Now one last thing about this, Do I tie pins 4 and 8 together with a .01 ceramic cap and then to a near by ground with another .01 cap, or do I individually tie them into a near by ground?
Do NOT tie them together directly (it would cause a short)! You can put an additional cap between the pins (some op amps need this for stability).
Old 14th November 2010
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Quote:
Originally Posted by living sounds View Post
Do NOT tie them together directly (it would cause a short)! You can put an additional cap between the pins (some op amps need this for stability).
Ok Thanx Got it now
Old 15th November 2010
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__________________Living Sounds.....Here is that pic of the Local Bypass......Finally Found it
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